But when you want to use this variable in a function, Splunk does not let you do it. Keeping the :s seems to be confusing for Splunk. When Splunk creates the fields for this variable, it shortens it to "SummationDeliveredL_x10k" automatically so that one can use it in the function as below.
I think I tried what you suggested. I removed ":" from the MINOR segmenters in segmenters.conf. When that did not work I also removed it from the MAJOR segmenters in all lines. It still did not work, even when I restarted splunk. The extracted field name in the Splunk GUI still ignores the part before the ":".
I am not sure what else to try. If you have any other ideas I would love to hear.